<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .w{width: 1200px;
            height: 800px;
            background-color: yellow;
            margin: 0 auto;
            /* 版心效果 1得有具体的宽度 2margin 0 auto */
        }

    </style>
</head>
<body>
    <div class="w">


    </div>
    
</body>
</html>